EPIDEMIOLOGY AND CONTROL - PowerPoint Presentation

Slide1

EPIDEMIOLOGYANDCONTROLOFCHOLERA

Slide2

BACKGROUND

Cholera, is a Greek word, which means the “

Gutter of the roof ”.

It is caused by bacteria:

Vibrio

cholerae, which was discovered in 1883 by Robert Koch during a diarrheal outbreak in Egypt.

V.

cholerae

has

2

major biotypes

: classical and El Tor

, which was first isolated in Egypt in 1905.

Currently, El Tor is the predominant cholera pathogen worldwide.

Slide3

Since 1817, there have been 7 cholera pandemics. The first 6 occurred from 1817-1923 and were caused by V. cholerae, the

classical biotype. The pandemics originated in Asia with subsequent spread to other continents.

The seventh pandemic began in Indonesia in 1961 and affected more countries and continents than the previous 6 pandemics. It was caused by V.

cholerae

El Tor.

Slide4

In 1992, a new serogroup – a genetic derivative of the EL TOR biotype – emerged in Bangladesh and caused an extensive epidemic.

This Bengal strain has now spread throughout Bangladesh, India, and neighboring countries in Asia.

Slide5

REPORTED CASESTotal MorbidityCholera cases are under reported because of poor surveillance (WHO estimates that only 5-10% of the worldwide cases get officially reported), but it’s likely to exceed ~1M cases annually, mostly from Africa and Asia

Total Mortality

Globally an estimated 120,000 deaths from cholera occur each year, with most of the cholera deaths occurring in Asia and Africa

Slide6

Disease SequelaeAmong people developing symptoms, 80% of episodes are of mild or moderate severity, however, severe cholera is characterized by acute diarrhea and vomiting which can lead rapidly to dehydration and death.Within 3-4 hours of the onset of symptoms, a previously healthy person may become

hypotensive and may die within 6-8 hours.

Slide7

Agent

Group A – Vibrio cholerae Serogroup 01

(which includes)

-

El-Tor - Classical or true : (Inaba,

Hikojima

, or Ogawa)

True cholera

vibrio

is demonstrated by:-

- presence of specific O antigen and

- no

hemolysis

of goat or sheep RBCs if added to suspension of these cells.

Group B – non cholera

Vibrios

.

(Non pathogenic to man)

Slide8

Most vibrio strains elaborate enterotoxin resulting in similar clinical picture - In any single epidemic one particular type tends to be dominant

(presently El Tor biotype

is predominant except in Bangladesh, where the Classical

biotype

has reappeared).

Slide9

Viability of Cholera

Vibrio

outside the body

- In tap water (

contam

. with

feces

)= 5 days

- In stool: (in summer) = 2 days

- In stool: (in winter) = 8 days

- In

corpes

= 4 wks

- In

clothings

= 2-6 days

- In dates (peelings) = 3 days

- In fish = 2-10 days

- In milk (raw) = 3 days

- In milk (boiled) = 10 days

Slide10

Man

- A patient during

incubation period

(faeces)

- A patient during

illness

(faeces &

vomitus

)

- A patient during

convalescence

(faeces)

- Contact through (faeces)

Reservoir Host

Slide11

Incubation period:

Few hours – 5 days.

“ The international I.P. is 5- days “.

Period

of communicability:

- For the duration of stool

+

ve

stage

(usually few days after recovery)

- Carrier state may persist for few months.

Infection 7-14 days

, but most people do not

become ill or show any symptoms

Only about

10-20% of infected

people

show moderate or severe symptoms. *NOTE: Effective antibiotic eg. (tetracycline) reduce the period of communicability.

Slide12

High density population,

Increased humidity,

Abundance of uncontrolled water supply,

High salinity and organic water contents.

**- An attack gives temporary immunity

(against a

homologus

serotype through a rise in agglutinating,

vibriocidal

and antitoxin antibodies which all lead to resistance).

WHO cholera 6th report stated factors favouring

endemicity

in India

Slide13

TRANSMISSION

Fecal-oral route through contaminated water & food.

The infectious dose of bacteria required to cause clinical disease varies with the source. If ingested

with water

the dose is in the order of 103-106 organisms

. When ingested

with food

,

fewer organisms

are required to produce disease, namely

10

2

-10

4

.

Person to person infection is rare.

Animals do not play a role in transmission of disease.

Slide14

V cholerae cause clinical disease by producing an enterotoxin that promotes the secretion of fluid and electrolytes into the lumen of the gut.

The result is

watery diarrhea with electrolyte concentrations

isotonic to those of plasma

.

The enterotoxin acts locally & does not invade the intestinal wall. As a result

few WBC & no RBC

are found in the stool.

V.

cholerae

is

unable

to survive in an

acid medium

.

PATHOGENESIS

Slide15

Fluid loss originates in the duodenum and upper jejunum; the ileum is less affected.

The

large volume of fluid produced in the upper intestine

, however, overwhelms the absorptive capacity of the lower bowel, which results in

severe diarrhea

. The colon is usually in a state of absorption because it is relatively insensitive to the toxin.

Slide16

SYMPTOMSVery rapid onset of vomiting and diarrhoea with large volumes of very watery

(rice water type) stools (>3 times a day)

Severe de-hydration, =

low pulse

,

undetectable blood pressure, sunken eyes, wrinkled hands and feet.

Slow recovery of shape after depression of skin

No urine output

Laboratory confirmation but count all suspected cases and treat

Slide17

DIAGNOSIS Confirmed by culturing Cholera vibrio of serotype 01 from faeces , or

Significant rise in titer of antitoxic antibodies, or

Presence of agglutinating or vibriocidal antibodies.

Slide18

Diagnosis of choleraTests that may be done include:

Dark field Microscopic examination Blood culture

Stool Culture

Slide19

AT RISK GROUPS All ages but children & elderly are more severely affected.

Subjects with blood group

“O

”

are more susceptible; the cause is unknown.

Subjects with reduced gastric acid.

Slide20

RISKY CULTURAL PRACTICES/ BELIEFSThe following beliefs about causes of cholera may reduce effectiveness of key messages :-

Witchcraft, eye, wind, climatic change cause the sicknessChildren’s stools are not dangerous

Soap is believed to wash away luck

The following practices increase risks :-

Anal washing is often not followed by hand-washing

Handshaking transfers bacteria directly from one person to the nextBurial ceremonies may spread disease

Slide21

Endemic 1. Cholera reservoir, constant or sporadic few cases

Epidemic. Triggered by factors. Reaches peak and then preventive measures dominate

Endemic 2. Continued levels higher than endemic 1 while person to person infection continues

TYPICAL CHOLERA CURVE

Slide22

WHEN DOES CHOLERA BECOME EPIDEMIC?After heavy period of rainfallWhen water temperatures riseWhen

normal diarrhoeal incidence increases Endemic cholera with good sanitation needs permanent source

of vibrio, but with poor sanitation higher

secondary transmission

can maintain endemic status.

Slide23

METHODS OF CONTROLPreventive measures:- 1- Sanitary disposal of human faeces

(maintenance of fly proof latrines). 2-

Protect, purify and chlorinate public water supplies.

(avoid cross

connectns

. with sewer syst.). 3- Control flies by spraying with insecticides. 4- Cleanliness in preparation of food,

5-

Pasteurize or boil milk

,

6-

Sanitary supervision of commercial milk production, storage and delivery

.

Slide24

CONTROL OF PATIENTS, CONTACT AND ENVIRONMENT:-Reporting to local health authority,Cleanliness in preparation of food,

Pasteurize or boil of milk and sanitary supervision of commercial milk productn. storage and delivery.

Slide25

Isolation or hospitalization with enteric precautions esp. for severely ill pts. eg

. (effective hand washing + fly control measures).

Disinfection of articles soiled with faeces or vomits of patients

(by heat, carbolic acid or other effective disinfectant).

Slide26

Contacts:- Surveillance

for 5-days.

- Chemoprophylaxis with tetracycline.

-

No immunization necessary.

- Investigate contacts with source of infection.

- Specific Rx:-

* Prompt

fluid replacement

using adequate volumes of electrolytes solutions, to correct dehydration.

Slide27

Epidemic Measures

1- Essential measures :

-

Hygienic disposal of human faeces.

- Adopting emergency measures to assure a safe water supply (boiling and chlorination).

- Good food hygiene.

Slide28

2- Two types of vaccines are available which provide high level of protection for several months against vibrio

cholerae serotype 01

.

( Of use for

travellers to endemic countries, but not yet used for public health purposes ).

3- Notification ( of WHO & adjacent countries) is required.

Slide29

4- Health education in personal hygiene. 5- Search for source of infection.

6- Specific measures during pilgrimage

season.

Slide30

EFFECTIVE FOOD HYGIENE MEASURES: a- Cooking food thoroughly & eating it while

still hot.

b- Preventing cooked food from being contaminated by contact with raw food (water & ice), or with contaminated

surfaces

or flies. c- Avoiding raw fruits or vegetables unless they are first peeled.

d-

Hand washing

after defecation, esp. before contact with food or drinking water.

Slide31

Key MessagesBad water is one source of cholera (disinfect source or stored water) but others, especially contaminated food (clean and cook well) and associated lack of hand washing

(essential times and methods for hand washing) should also be highlighted.

Rapid transfer to clinics or use of ORT clinics speeds up treatment and reduces cross infection.

Re-hydration

as early as possible saves the most lives- water quality in OR is of little importance

Good surveillance systems can identify causes and reduce infection rates